Shiftable transmissions for motor vehicles have long been known in many different forms. In the past, a shiftable transmission was primarily understood to be a manually-shiftable transmission, in which the driver of a motor vehicle equipped with this type of shiftable transmission selects the shift path and performs the gear shift operation by hand via a shift lever. In addition to these manually-shiftable transmissions, it has also been known in the meantime to use automated shiftable transmissions when the operation of selecting and shifting the selected gear stage is executed, for example, according to programmed control by actuators provided in the shiftable transmission.
During operation, an automated shiftable transmission of this kind is subjected to normal wear and tear on its component parts, e.g., the synchronizing means, which wear and tear can lead to displacement of the middle synchronization position. The middle synchronization position is defined herein as a mean position value during the synchronization operation. The blocking position of the synchronizing means can vary somewhat from shift operation to shift operation, because the shift sleeve can engage in the synchronizer ring differently and unpredictably from shift operation to shift operation.
However, accurate knowledge of the synchronization position is important, as the synchronization position should be quickly reached by the shift actuator in order to shorten the shift time. In addition, the shift actuator should also quickly arrive at its end position (i.e., the gear engaged position) at the end of the synchronization operation.
When the shift actuator reaches the synchronization position, the synchronizing means exerts a blocking effect on the shift actuator as a result of the synchronization operation, which leads to an increase in the load current of the actuators. It has already been known to detect the start of the synchronization by this increase in the load current.
However, detecting the load current is comparatively complicated and expensive and furthermore, can only produce a result with regard to a change of the synchronization position within the bounds of a continuous determination of the actuator position, as the position of the actuator when the load current increases must be known.